1. Field
Embodiments relate to a robot arm and a method of controlling the same, and more particularly to a robot arm having high back-drivability to interact with a human being, which is safely stopped, and a method of controlling the robot arm.
2. Description of the Related Art
In general, machines, which conduct motions similar to those of a human being using an electrical or magnetic action, refer to robots. Initial robots were industrial robots, such as manipulators or transfer robots, for work automation and unmanned operation in a production field, which perform dangerous work, simple repetitive work, or work requiring large force in place of a human being. Recently, humanoid robots, which have a joint system similar to that of a human being, live together with the human being in human working and living spaces, and provide various services, have been vigorously researched and developed.
Such a humanoid robot includes robot arms having high back-drivability to interact with a human being in daily life, and each of the robot arms is formed in a single rod shape or has a plurality of joints. The back-drivability denotes a degree of the movement of the robot arm, when external force is applied to the robot arm under the condition that current is not applied to a joint motor (generally, an actuator) and thus no torque is generated.
Therefore, under the condition that power is cut off, the robot arm having high back-drivability is easily moved using external force, a torque applied to a joint of the robot arm is easily measured through motor current due to small kinematical friction of the joint, and the stiffness of the robot arm is adjusted through an impedance control such that the robot arm achieves flexibility and thus is capable of performing an interaction with a human being (for example, a hug with the human being).
However, in case that power supplied to the robot arm having high back-drivability is cut off in an emergency, in which the operation of the robot arm is stopped, the robot arm (particularly, the tip of the robot arm) is dropped down by gravity due to the small friction of the joint. Thus, in case that power supplied to the robot arm is cut off, when the robot arm is located at a low position, no trouble is caused, but when the robot arm is located at a high position, the robot arm is excessively moved.